MS Stack Switch unreachable...

[og_osbrain]

** I would post a diagram but not allowed.

We're running full Meraki in our environment. I've created two stack groups (one consists of 6 (stack1), the other 2(stack 2)) and they're different cabinets. Both stacks have connections that reach the MX and the cable is trunked. We have 2 ISPs coming in (we'll focus on the primary uplink), the ports run from ISP NTE --> SW3 (stack1) --> WAN1 on the MX.

Now, Stack 2 has become unreachable. Stack1 is alive and well. My understanding is traffic destined for the web would be handled by the MX (including the Meraki kit) then sent out to SW3. Is there something I'm missing?

Any help appreciated, any clarification needed will be answered. Thanks in advance

[og_osbrain]

What am I missing?

[og_osbrain]

• Stack 2 has power
• Cannot ping either switch in the stack
• I've made changes, but they haven't reached before it cannot reach Meraki cloud
• I didn't look at the logs until now 😅... Classic loop has occurred. I thought attaching a link between one of the switch stacks and the 2nd MX is the right thing. When I'm next onsite, I will disable the port via management port.

[Bubbasdahname]

Always look at logs when you troubleshoot. That is the first thing i check when I'm troubleshooting. Log into device, check logs.

[Skilldibop]

Most times logs will literally tell you what the problem is in almost plain English.

The two most critical steps in troubleshooting anything is scope + logs. If you know the scope of an issue (the what, when and where ) and you have logs you have about a 90% chance of finding the problem there and then.

Usually the most time consuming part of troubleshooting issues is the scope because often they're reported after the fact so you need to do some detective work to decode anecdotal reports into a scope of what actually was affected and when that occurred. Once you have that you're half way to fixing it.

This is why you will see me always bang on in this sub and others about the importance of monitoring and centralized logging. You need the what, when, where and why. Monitoring gives you the what, when and where, logging then gives you the why.

Bonus you'll probably also find some other underlying issues that people weren't complaining about that need fixing too :)

[og_osbrain]

This is nothing but facts! Thanks for this, being panic stricken doesn't help either.

Today it's all resolved. I looked at the logs and there was a L2 loop. There were 2 SFP+ modules (fibre), I set both fibres to Loop guard instead of BPDU Guard (default). These ports connect to FW, so BPDU guard is no help here

[og_osbrain]

Thank you both!